I have had dealings with carphonewarehouse regarding exactly this sort of problem, and hears what I done.
I e-mailed carphonewarehouse customers services and told them that the present contract I had with them, (assuming your old phone is from them) I could no longer afford to run it? within the hour a sales person came back too me and asked me what I intended doing now, so I said…get another phone from elswere…….he purposed the following to me:
As I was a good customer they would like to give me a loyality credit of £240 in my account….meaning I could have free use o my phone for one year, and they would take the credit out of the £240 every month.
About £25 per month. I done this and had free use of my phone for one year…….But beware!! you must keep account of every penny you use and get on your monthly bill from them, as they do not inform you when its due to end and you coul end up paying a lot of money oo them….there is no contract,
There is also another way, which is tell them that you like to end all contracts with them and ask them for a free SIM and also ask where you can get a PAC code to change your present number to the new SIM…..Unfortunately this is on pay as you go…sory I could not be more tooyou